The invention relates to an improved mechanism and improved methods for pressing by product bed comminution.
In the operation of roller crushing, a new and unique form of crushing which has been referred to as product bed comminution or interparticle crushing has been discovered such as disclosed in Schoenert U.S. Pat. No. 4,357,287 and Beisner et al U.S. Pat. No. 4,703,897. This art, as described and claimed in these patents, involves an operation wherein the gap width and force applied between the rollers is such that a crushing fineness is attained by the particles entering the nip mutually crushing one another and forming incipient cracks in the grains. This process and this equipment has resulted in new and unforeseen energy conservation with improved crushing.
Accordingly, the present invention relates to improvements in the art of interparticle crushing or product bed comminution to utilize the advantages of the development and to improve on the process to the extent of having improved draw-in qualities in the nip, of protecting the roller surfaces which are exposed to extraordinarily high stressing and wear and to provide an overall improvement.
In roller crushers and roller mills, brittle grinding stock is drawn into the nip between two rotatable rollers rotating in opposite directions. In interparticle crushing, the individual particles of the grinding stock are drawn into the nip by friction crushing one another therein in a product bed comminution and the material is compressed between the roller surfaces with the application of an extremely high pressure such as disclosed in European Patent 0 084 383.
In this operation, the roller surfaces are exposed to extraordinarily high stressing and high wear. An improvement which has been done is to armor the roller surfaces such as welding layers of hard metallic materials of welding beads welded side-by-side onto the base roller. Another structure which has been adopted is that a wear-resistant cladding of cast or rolled material is applied to the base roller to provide a hardened outer surface. These structures, such as the roller armoring, require a time consuming surface layer welding of annular plies or involve helical welding and increase the cost of the machine.
In order to improve the product draw-in capability of the pressing rollers that must draw the product into the nip by friction and compress it, it is known to provide the armored roller jacket with a plurality of profiles having the shape of welding beads arranged V-shaped on the closed hard cylindrical surface in an additional manufacturing step as disclosed in the aforementioned European Patent 0 084 383. In interparticle crushing of especially abrasive materials such as ores, it has been shown that the risk is not excluded that the roller surface will wear relatively quickly during operation due to the creation of trough-shaped erosion or, excavations in the regions between the profiling welding beads that are welded on at a distance from one another.
The closed, hard outside shell of the armored roller jackets can be over-stressed due to the formation of pressure islands in the nip filled with product material to be pressed with high localized point stressing of the rollers. Surface cracks can lead to the progression of cracks into the base roller member and the hard profile parts that are welded onto the roller can be laterally pinched off given a soft underlayer. The risk is thereby present that the outwardly salient, welded-on profiling welding beads can at least partially break off given high point stressing.